Method and apparatus for chemically transforming gases

ABSTRACT

In a system in which a gas in a supersonic stream is chemically transformed by a principal electric discharge, an auxiliary discharge first ionizes the gas in the stream.

United States Patent [72] Inventors Michel Denis Marly 1e Roi; MauriceBarillot, Verneuil en lhlatte, both of France [211 App]. No. 830,320

[22] Filed June 4, 1969 [45] Patented Nov. 16, 1971 [731 AssigneesInstitut De Recherches De La Siderurgie Francaise St. Germain en Laye;Societe Chimique Des Charbonnages Paris, France [32] Priority June 6,1968 [3 3 France [54] METHOD AND APPARATUS FOR CHEMICALLY TRANSFORMINGGASES 4 Claims, 4 Drawing Figs.

[52] U.S.Cl 204/171, 204/323, 204/165, 204/170 [51 1 Int. Cl .C07b29/06,(07c 5/18. BOlk H00 [50] Field of Search 204/164,

[56] References Cited UNITED STATES PATIENTS 3,344,051 9/1967 Latham eta1 204/327 X 3,347,774 10/1967 Myers 204/327 X 3.003939 10/1961 Rouy etal.... 204/164 3,051,639 8/1962 Anderson 204/171 3,280,018 10/1966 Denis204/164 3,308,050 3/1967 Denis 204/164 X 3,537,965 11/1970 Keckler cl al204/171 FOREIGN PATEN'ITS 970,767 9/1964 Great Britain 204/171 PrimaryExaminer F. C. Edmundson Attorney-Kurt Kelman ABSTRACT: In a system inwhich a gas in a supersonic stream is chemically transformed by aprincipal electric discharge, an auxiliary discharge first ionizes thegas in the stream.

PAIENTEnuuv 16 1911 SHEET 2 BF 3 Mi Ewan: Mum DEN/5 MAumce' BARILLDT M4Mex/T METHOD AND APPARATUS FOR CHEMICALLY TRANSFORMING GASES BACKGROUNDAND SUMMARY OF THE INVENTION The present invention relates to a processand apparatus for ionizing a gaseous stream moving at supersonic speedand wherein a high-power electric discharge is produced to cause achemical transformation of the gas or gases constituting the stream.

In a conventional process of this type, a stream of gas is brought tosupersonic speed and is subjected to an electronic discharge produced byan electrode positioned along the axis of the gas stream and connectedto a high-voltage generator. If the voltage variations duringalternation are examined in an alternating discharge at the boundariesof the elements between which the discharge is produced, it is foundthat the voltage rises to a value V then drops suddenly, and finallyremains constant at an average value V until the end of the alternation.This phenomenon is repeated at each alternation. These voltagevariations may be explained by the fact that, since the gas stream isnonconductive, the voltage rises until it has reached the point wherethe electrons produced have sufficient energy to ionize the gas. At thispoint, the gas becomes conductive and the voltage drops suddenly tovalue V which corresponds to the value of the voltage required tomaintain the discharge in the ionized gas. Thus, a high starting voltageV, must be attained at each alternation although a much lowermaintenance voltage V, suffices to maintain the discharge. Experiencehas shown V to be substantially equal to about 3 V Therefore, if aconstant discharge is to be produced in a supersonic stream of gas,voltage generators must be employed which have a capacity of generatingthree times as much voltage to start the electric discharge as isrequired to maintain it. it is also necessary to limit the electriccurrent by incorporating into the discharge circuit either resistances,which results in a loss of power, or self-induction coils, which makesthe cos 1 of the installation poor. On the contrary, if the gaseousstream constantly includes carriers of the electric charge, i.e. if itis ionized, it is possible to utilize a generator which delivers avoltage not much higher than V, to produce the desired electricdischarge.

In another known process of this type, a first electric discharge isproduced in a supersonic gaseous stream between a tuyere, from which thestream is discharged, and an axially extending electrode, and use ismade of the ionization of the gas resulting from the first electricdischarge to produce a second electric discharge in a recompressioncollector beyond the shock wave, i.e., in a zone where the stream isagain subsonic to cause certain chemical transformations in the gaseousstream.

However, it has been found that in certain chemical reactions, forinstance in the transformation of butane into acetylene, a discharge inthe latter zone caused a further chemical transformation so that, at theoutlet of the recompression collector, a large proportion of carbon andhydrogen was found. In other words, the reaction had proceeded to thecomplete decomposition of the gas, the elements being consideredundesirable byproducts in this reaction.

It is one of the primary objects of this invention to produce electriccharge carriers in a gaseous stream moving at supersonic speed beforeproducing an electric discharge in this stream capable of causingchemical transformations in the gas or gases of the stream.

It is another object of the invention to produce well-defined compoundsin the chemical transformations.

The above and other objects and advantages are accomplished according tothe present invention by ionizing a gaseous stream moving at supersonicspeed by means of an auxiliary electric discharge, and producing aprincipal electric discharge in the ionized stream to cause chemicaltransformations in the gas. The gaseous stream is discharged from asupersonic tuyere or nozzle and the chemically transformed gas isreceived in a collector chamber. The invention provides a supersoniccell between the tuyere and the gas collector and this cell has aconstriction at the level where the shock waves produced at the tuyereoutlet cause deviation in the direction of the gas stream. An auxiliaryelectric discharge is produced between an axially positioned principallelectrode, which is enveloped by the gaseous stream, and an auxiliaryelectrode positioned outside the gaseous stream. In this manner, theions produced by the auxiliary electric discharge and entrained by thegaseous stream along its periphery are carried into the interior of thestream by the constriction in the cell.

According to one embodiment of the present invention, the auxiliaryelectric discharge is produced upstream of the constriction but close tothe collector element.

In accordance with another embodiment of this invention, the supersonictuyere is brought to an electric potential such that the potentialdifference between the nozzle constituting the auxiliary electrode andthe axial electrode is higher than the potential difference between theaxial electrode and counter electrode provided by the apparatus. Theauxiliary electric discharge is produced at the end of the supersonictuyere between the tuyere and the axial electrode surrounded by thegaseous stream. The principal electric discharge is produced in thatpart of the recompression collector where the shock wave is produced.

in yet another embodiment of the invention, the voltage producing theauxiliary discharge is of a different phase than the voltage producingthe principal discharge so that the intensity of the auxiliary dischargeis at a maximum when the voltage producing the principal dischargereaches a value ap proximating the voltage necessary to sustain thedischarge in the ionized gas.

in the apparatus of the present invention, a supersonic tuyere isconnected in a fluidtight manner to an expansion chamber leading to anelement of gas recompression positioned in line with the outlet of thetuyere. An electrode is positioned axially in the tuyere and extends tothe inlet of the gas recompression chamber. The apparatus comprises anauxiliary electrode which produces an electric discharge through thegaseous stream between the axially positioned electrode, which issurrounded by the stream of gas, and the auxiliary electrode.

In accordance with one embodiment of the apparatus of this invention,the auxiliary electrode is positioned in the gas expansion chamber andis constituted by a support of electrically conductive material. Thesupport is glidably but fluidtightly arranged in a guide mounted in thewall of the expansion chamber, and is electrically insulated from theguide, from the expansion chamber and from the recompression chamberwall. The auxiliary electrode support has an extension at one endprojecting into the expansion chamber, the extension being of a metalsuitable for producing and sustaining an electric discharge between thismetallic extension and the axially positioned electrode.

The extension is preferably a pointed metallic pin fixed to the end ofthe conductive support and being eccentric in respect of its axis. Thepointed pin may be inclined to the support axis and fixed to the centerof the support end.

According to another embodiment of the invention, the conductive supportmay be arranged for rotation about its axis in the guide.

in yet another embodiment, the distance between the noninsulated pointsof the auxiliary electrode from the nearest points of the supersonictuyere and from the recompression chamber wall exceeds the distanceseparating the noninsulated points of the auxiliary electrode from theaxial electrode.

In accordance with still another feature of the present invention, theauxiliary and the axially positioned electrodes are connected to theterminals of the same high-voltage source.

In one preferred embodiment, the tuyere may be of an electricallyconductive material to constitute the auxiliary elec' trode, and iselectrically insulated from the remainder of the apparatus, electricallyinsulating means being provided to connect the tuyere to an electriccurrent generator. This means may be constituted essentially by a rod ofelectrically conductive material disposed in a protective guide ofelectrically insulating material. This protective guide may define acavity holding biasing means, such as a spring, to maintain the rodconstantly in contact with the supersonic tuyere.

With this method and apparatus, ionization of the gas is first producedby the spark from the auxiliary electrode across the gas stream andupstream of the principal electric discharge, between an axiallypositioned electrode surrounded by the gas stream and an auxiliaryelectrode electrically insulated from the other components of theapparatus.

The introduction of ions into the interior of a gaseous stream moving atsupersonic speed encounters certain obstacles due to the very highvelocity of the gas molecules. Experience has shown that a gas jet or agas stream moving at supersonic speed has physical characteristics quitedifferent from those of a gas at rest or moving at slow speed Moreparticularly, an electric discharge or spark enters a supersonic gas jetwith great difficulty and is produced more readily between the auxiliaryelectrode, which is positioned outside the gas stream, and thecompression chamber walls, the pressure in the chamber being low.Furthermore, the ions produced by the discharge have a tendency, due tothe high speed of the jet, to remain localized on the periphery of thegas stream. Finally, in a gas moving at supersonic speed, a turbulencecannot be carried back up the high-velocity stream and any suchturbulence will, therefore, appear only downstream.

We have found that, in first ionizing a supersonic gas jet and thensubjecting the ionized jet to an electric discharge of greater power inthe zone of the shock wave, the discharge will be concentrated in theshock wave, i.e., in a surface having practically no thickness (a fewmicrons), which surface constitutes an extremely sharp transitionbarrier between the supersonic flow and the subsonic flow. It is thuspossible to produce acetylene in high yields from saturated hydrocarbonscontaining at least four carbon atoms, such as butane,

This may be done by placing the end of the axially positioned electrodeat the inlet of the recompression collector. If the electrode end is inthe zone of the gas stream where the shock wave is formed due to thelaws of aerodynamics, it facilitates the formation and stabilization ofthe shock wave which attaches itself to the electrode end. The largestpart of the energy of the electric discharge is thus concentrated in thesurface of the shock wave, and the gases to be chemically transformedare subjected to the discharge for an extremely short time, i.e., thetime required for the spark to pass through the shock wave. Therefore,the transformation of an important fraction of a hydrocarbon, forinstance butane, into acetylene may be obtained without a prolongedaction of the spark on the material, which avoids the possibledecomposition of the acetylene by the action of the electric discharge,as has occurred in many conventional processes of this type.

We have also found that, under the above-described conditions, theauxiliary electric discharge is produced between the end of thesupersonic tuyere and the axial electrode, and that the ions follow theexterior surface of the gas jet, i.e., the surface of the firstsupersonic cell which is formed at the outlet of the tuyere, and theypenetrate into the jet stream at the first constriction they encounter,i.e., behind the first supersonic cell. Thus, the recompressioncollector and the tuyere may be positioned at a closer distance althoughthis distance must be large enough to provide at least one entiresupersonic cell and to avoid producing a direct electric dischargebetween the tuyere and the collector.

Another advantage of this invention is that there is no problem ofpositioning the auxiliary electrode since this may be the tuyere itself.Thus, gases of all types may be used and may form supersonic cells ofvariable lengths under different pressures while maintaining theauxiliary electrode, i.e., the tuyere, in the same position.

BRIEF DESCRIPTION OF THE DRAWING The above and other objects, advantagesand features of the present invention will become apparent from thefollowing detailed description of certain embodiments thereof, taken inconjunction with the accompanying drawing wherein FIG. 1 schematicallyshows a supersonic cell and the shock waves produced by a tuyere;

FIG. 2 is a sectional view of one embodiment of the apparatus, includinga diagram of the electric circuit;

FIG. 3 is a sectional view showing the mounting of the auxiliaryelectrode in this embodiment of the apparatus; and

FIGv 4 is a view similar to that of FIG. 2 and showing anotherembodiment.

DETAILED DESCRIPTION In the practice of the invention, it is essentialto establish a stable steam of gas moving at supersonic speed, in whichchemical reactions are produced by an electric discharge passing throughthe stream. The stream must not be disturbed in any manner, which forcesthe auxiliary electrode to be positioned near, but outside of, thegaseous stream. The gas stream cannot be considered as a cylindrical jetof uniform section. In practice, due to manufacturing imperfections, thetuyeres are not of the contemplated ideal cross section, and one orseveral supersonic cells similar to those indicated in FIG. I areproduced.

As shown in FIG. 1, such a supersonic cell comprises a constriction S ofthe gas stream at a predetermined distance from the plane of the gasoutlet of tuyere l, at which point there is an inward refraction ofshock waves 2 which are produced at the outlet of the tuyere, and adeviation in the stream due to the shock waves. For given operatingconditions, one or more such supersonic cells may be produced byadjusting the distance between the plane of the outlet of tuyere l andthe gas collector. Generally, the distance of the collector from thetuyere is so adjusted that a single such cell is produced.

We have found that certain properties of these cells facilitate passingan electric discharge through the stream of gas and to ionize the samehomogenously by means of an auxiliary electric discharge whilemaintaining the auxiliary electrode outside the gas stream so as not todisturb its supersonic flow.

In fact, if the auxiliary electrode is placed close to the gas streamand upstream of the point of constriction of the stream, an electricspark may be passed through the stream between an electrode axiallypositioned in the center of the stream and the auxiliary electrode. Thespark produces an envelope of ionized gas around the periphery of thegaseous stream. As soon as this ionized stream reaches the point ofconstriction, it is absorbed and dispersed into the interior of the gasstream beyond the point of constriction. Under the action of therefracted shock waves and the deviation of the jet due to the shockwaves, as seen in FIG. 1, the ions are entrained and dispersed throughthe stream of gas moving at supersonic speed. A very short distancedownstream of the point of constriction, the carriers of electriccharges are thus distributed completely in the stream, and it is nowpossible to produce a powerful electric discharge in the gas withoutusing very high voltages.

It will be appreciated that this result cannot be obtained withoutforming the described and illustrated supersonic cells, and that it isequally essential that the positioning of the auxiliary electrode mustmeet certain requirements.

First of all and to facilitate the electric discharge, the auxiliaryelectrode must be positioned as close as possible to the axial electrodewithout, however, disturbing the supersonic flow of the gas stream. Itwill be easiest to adjust the position of the auxiliary electrode sothat it does not perturb the flow of the gas stream by measuring the gaspressure in the expansion chamber. If it is found that the pressurerises, the auxiliary electrode touches the periphery of the gas streamand perturbs the flow thereof.

Secondly, it is important that the ions reach the region where theprincipal electric discharge is produced, and that the auxiliarydischarge is not completely or even partially produced between theauxiliary electrode and another com ponent of the apparatus.

The lateral position of the auxiliary electrode along the gaseous streamis, therefore, a compromise between these two requirements, it beingunderstood that it must always be placed at the level or upstream of theconstriction zone. For the given life of the ions and a given speed ofthe gas stream, the ions flow only a predetermined distance to the zonewhere the principal electric discharge is produced. This conditiondefines the maximal distance between the zone of the principal electricdischarge and the auxiliary electrode beyond which the auxiliarydischarge loses all effectiveness. However, the auxiliary electrode maynot be positioned too close to the gas collector to avoid an electricdischarge between the two, without such a discharge penetrating into thegas stream.

In view of the above, the point of constriction in the gas stream mustbe determined for given operating conditions of the supersonic tuyere.This determination may be made experimentally, either visually byproducing an electric discharge between the axially positioned electrodeand the outlet of the supersonic tuyere, or by measuring the operatingpressure in the expansion chamber and progressively displacing the axialelectrode; when the free end of this electrode reaches the level orplane of the constriction, a sudden rise in the pressure will beregistered. in this way, the position of the electrode readily indicatesthe position of the point of the constriction of the gas stream inrespect of the plane of the outlet of the tuyere for given operatingconditions.

The position of the point or plane of constriction may also becalculated by known equations of the thermodynamics of flowing gases. Inthis manner, the desirable distance of the auxiliary electrode from theplane of the tuyere outlet may also be calculated as a function of thegeometric characteristics of the tuyere and the aerodynamic behavior ofthe gas flow. It has been experimentally determined that this distancemay be calculated by means of the equation wherein yr; is the Machnumber attained by the stream of gas and k is a constant which dependssolely on the diameter of the divergent outlet of the tuyere and itsrelation to the diameter of the electrode axially disposed within thegas stream.

The coefficient k may be defined by k=f(D/dXD, wherein D is the diameterof the divergent tuyere outlet and d is the diameter of the axialelectrode.

The Mach number is calculated from the pressure of the gas introducedinto the tuyere and the pressure of the gas in the expansion chamber bythe following well-known equations:

wherein T is the temperature of the gas before expansion, T is thetemperature of the gas after expansion, P, is the pressure of the gasbefore expansion, and P is the pressure of the gas after expansion,y=C,,, wherein C is the specific heat of the gas at constant pressureand C is the specific heat of the gas at constant volume.

If the function f(D/d) has been experimentally determined for a givenratio D.-d, the position of the auxiliary electrode may be calculatedfor any dimensions and aerodynamic conditions of the tuyere since theposition of the constriction plane or point is determined by the sameconditions. Thus, under the given conditions, homo'genous ionization ofa supersonic gas stream may be obtained.

Referring now more particularly to the embodiment of the apparatus shownin FIG. 2, there is shown a supersonic tuyere or nozzle 4 which carriesgases at supersonic speed into an expansion chamber defined by wall 5whence the gas stream 19 moves into a recompression chamber dlefined bywall 6. The expansion and recompression chambers are in axial alignmentwith the axis of the supersonic tuyere 4 which is mounted in a coaxialcavity 7 defined by cylindrical support 8. The length of cavity 7exceeds that of the tuyere 4 so that an empty chamber 9 is formed in thesupport 8 rearwardly of the tuyere. A tubular inlet conduit 10 opensinto chamber 9 wherethrough the gas to be treated is supplied to thetuyere. A principal electrode 11 is axially positioned within theoutwardly flared axial bore of the tuyere 4, extending through axialbore 12 in the tuyere support 8 to the inlet of the recompressionchamber constituted by the outwardly flared axial bore in the wall 6.Electrode 11 is perfectly centered along the aligned axes of the tuyereand the recompression chamber, being mounted in bore 112 by means of anelectrically insulating plug 13 whose outer diameter corresponds exactlyto the diameter of bore 12 so as to provide a fluidtight mounting :forthe electrode. The tuyere support 8 is fluidtightly mounted in the bore141 of wall 5 and the tube 6, which defines the recompression chamber isalso fluidtightly mounted in the bore 15 of the wall 5. Thus, the gasjet moves at supersonic speed through fluidtight treatment zones.

An auxiliary electrode 16 is mounted in the wall 5 by means offluidtightly fitting, electrically insulating plug 17, extendingradially into the expansion chamber between the outlet of the tuyere 4iand the inlet of the recompression chamber. The noninsulated end 18 ofthe auxiliary electrode is disposed perpendicularly to the jet 19 andclose thereto.

The auxiliary electrode 16 is connected to one terminal 20 of ahigh-voltage generator constituted by transformed 21 whose otherterminal 22 is connected to principal electrode 11. The electric supplycircuit for the electrodes includes a self-induction coil 23 designed tolimit the intensity of the auxiliary electric discharge. The principalelectrode 11 and the electrically conductive wall 6 defining therecompression chamber are respectively connected to a source ofalternating voltage constituted by transformer T which permitsproduction of an electric discharge in the gas stream between electrode11 and the recompression chamber wall.

According to one embodiment of the apparatus hereinabove described, thediameter of the flaring bore of tuyere 4 is 6.8 mm. at the outlet end,and the diameter of the rod electrode 11 is 3 mm. The throughput of thetuyere is 4 liters of butane per second when the butane gas is suppliedto the tuyere through inlet pipe 10 at a pressure of 5 atmospheres.Under these operating conditions, the pressure in the expansion chamberis mm. Hg, i.e., 0.2 atmospheres. The Mach number X attained by thegaseous stream is accordingly calculated at 2.62.

These parameters make it possible to calculate the distance theauxiliary electrode 16 should have from the plane of the tuyere outletso that the auxiliary electric discharge takes place solely between theprincipal and auxiliary electrodes. Using the above-indicated equationand inserting the above dimensions and fD/d=0.7, the distance L=0.7 X6.8w/(2f62) 'l=l 1.5 mm.

In this example, tension 1 equals 3,600 volts and tension V equals 900volts. Transformer T is capable of delivering an alternating voltage of1,100 volts. Transformer 21 is capable of delivering an alternatingcurrent of 0.1 ampere at a voltage of 5,000 volts. The current intensitybeing limited by self-induction coil 23, the transformer is fed by athreephase 220 V feed circuit, and another power source feeds theprincipal transformer T so that the intensity of the auxiliary electricdischarge is at a maximum when the voltage used to produce the principalelectric discharge reaches a value in the neighborhood of that needed tomaintain the discharge in the ionized gas.

This example clearly illustrates the usefulness of the auxiliaryelectrode feeding the auxiliary electrode with a current of 0.1 A. at5,000 v. permits the use ofa current of A. at 1,100 v. to produce theprincipal discharge. 1n the absence of an auxiliary discharge, it wouldhave been necessary to use a transformer having an output of 20 A. at3,600 v. to produce the principal discharge.

FIG. 3 illustrates the structure of a useful auxiliary electrode indetail, the electrode being mounted in the wall 24 defining theexpansion chamber. The electrode is constituted by a cylindrical supportrod 25 of electrically conductive material to whose one end is fasteneda pointed metallic pin 26 of a material capable of sustaining theauxiliary electric discharges, the selected material being tungsten inthe illustrated example. The point 26 constitutes the active" portion ofthe auxiliary electrode because the discharge takes place between thisportion and the principal electrode 11. As shown, the point 26 iseccentric in respect to the axis of the electrode support rod 25.

A metallic tube 27 is soldered to the wall 24 which defines an obliquebore forming a seat for the tube 27 and leading to the orifice 28opening into the expansion chamber, the tube 27 serving as a guide forthe auxiliary electrode support rod 25. The support rod is encased inelectrically insulating sheath 29 which is held in fluidtight engagementwith the support rod by means of a toric gasket 30 positioned in anannular groove in the interior wall of tube 27. The outer end of theinsulating sheath 29 has a collar 31 forming an abutting should inengagement with the outer end of the tube 27. The support rod 25 definesan annular groove 32 wherein there is positioned a toric gasket 33 toassure the fluidtight seal between the rod 25 and the guide tube 27. Asleeve 34 is screwed over the outer end of tube 27 and engages thecollar 31 of the insulating sheath so as to hold the same againstdisplacement. A metallic head 35 is screwed into the threaded axial boreof sleeve 34 and its axial bore aligned with the axial bore in guidetube 27 forms the guide for the outer portion of rod 25. A connector 36connects the rod to the electric feed circuit described in connectionwith FIG. 2.

it will be understood that this mounting permit axial displacement ofthe rod 25 in guide tube 27 without in any way damaging thefluidtightness of the arrangement, and thus to adjust the point 26 inrespect of the axis of the gaseous stream. Further adjustment ispossible by rotating the electrode rod in its support, such rotationcausing a displacement of the eccentric point 26 along the axialextension of the gas stream, thus enabling the auxiliary electricdischarge to be fine tuned" for best results.

The same result may be obtained, for instance, by arranging theauxiliary electrode perpendicularly, instead of obliquely, in the wallof the expansion chamber, and positioning the point 26 obliquely at theinner end of the support rod 25, the point extending radially outwardlyfrom the axis of the rod.

Another embodiment of the apparatus is shown in H0. 4. This comprises atungsten tuyere or nozzle 38 carrying a gas at supersonic speed toexpansion chamber 39 whence it flows into a recompression chamberdefined by tubular wall 40. In this embodiment, the tuyere itselfconstitutes the auxiliary electrode and tungsten is particularly suitedfor this purpose because it is refractory and a good electricalconductor. How ever, other materials, such as steel or graphite, mayalso be used.

A cylindrical steel support 41 fluidtightly holds the nozzle andrecompression chamber, the nozzle 38 being electrically insulated fromthe support 41 by sleeve 42 of mica or glass. it will be noted that theouter end 420 of the insulating sleeve projects beyond the plane of thenozzle outlet 38a to prevent parasitic discharges between the nozzle andthe steel support 41.

The general arrangement is in many respects similar to that of FIG. 4and will, therefore, not be described again, the gas to be treated beingagain supplied through supply pipe 44 delivering the gas into chamber 43rearwardly of the nozzle.

The principal electrode 45 extends axially through the nozzle 38 to theinlet of the recompression chamber, in this manner to produce and tostabilize the shock wave at the recompression chamber inlet and toattach it to the inner end of the principal electrode 45, due to thediscontinuity in the gas flow created by the end of the electrode. Thus,the principal electric discharge is produced at this point of gas jet 66and is concentrated in the shock wave, i.e., in a very small volume ofgas having a thickness of the order of two microns. in other words, forall practical purposes, the discharge is concentrated on the surface ofthe gas stream. This concentration of the discharge on the surface maybe explained by the blast due to the speed in the supersonic zone and bythe fact that the shock wave constitutes for the discharge a barrierwhich may be very easily broken due to the transition to the subsoniczone in which the discharge is not readily produced. it is this verylocalized discharge which transforms the butane gas into acetylene whenbutane is fed to the system.

The electrode is fluidtightly centered in the tuyere 38 by means ofinsulating plug 46 which may be a cement consisting of asbestos andagglomcrates.

A brass rod 47 electrically connects the tuyere 38 to terminal 48 of ahigh-voltage generator constituted by transformer 49 whose otherterminal 50 is connected to principal electrode 45. While brass ispreferred because of its good electrical conductivity and highmechanical resistance, other conductive materials, such as copper ortungsten, may be used for rod 47.

The connecting rod 47 must be effectively insulated from wall 41 whereinit is mounted to avoid any parasitic discharges therebetween. Theillustrated insulation includes sleeve 51 which may advantageouslyconsist of polyfluorethylene containing a glass fiber filler. Thismaterial provides not only very good insulation but also enables the rod47 to glide readily in the sleeve. To assure good contact between theconnecting rod and the tuyere 38, a compression spring 52 is mounted ina seat 54 in the insulating sleeve, the spring pressing against ashoulder 53 and the spring seat being closed by plug 55 which is boltedto the sleever at 56. The compression spring will hold the slidableconnection rod 47 at all times in good contact with the tuyere.

The insulating sleeve 51 is screwed into the insulating sleeve 42 and agasket 57 further assures fluidtight connection between the insulatingparts. The insulating sleeve 51 is mounted in a cylindrical block 58 ofsimilar material as plug 46, this block being mounted on the support 41by bolts 59.

The interior of the apparatus is further fluidtightly separated from thesurrounding atmosphere by gaskets 60 and 61 between the sleeve 51 andthe plug 55, and between the rod 47 and the plug 55. Similarly, gaskets62 are disposed between guide sleeve 51 and block 58, and gaskets 63 areprovided between the block and the wall 41.

One of the advantages of this mounting is that the insulating sleeve forthe connecting rod is screwed into the insulating sleeve for the tuyere,and may be readily disassembled without interfering with the fluidtightseal of the interior of the apparatus from the atmosphere. The block 58may also be readily removed.

As in the other embodiment, the electric feed circuit for the electrodesincludes a self-induction coil 64 and a principal transformer 65. Theauxiliary discharge is limited to a current of 0.2 A. at 2,500 v. Thecurrent fed by transformer 65 is a 20 A. at 1,100 v. The potentialdifference between the supersonic tuyere, i.e., the auxiliary electrode,and the principal or axial electrode is 2,500 v. while the differencebetween the axial electrode and the mass of the apparatus, i.e., therecompression chamber wall, is only 1,100 v.

While the invention has been described in connection with certain newpreferred embodiments, it will be clearly understood that manyvariations and modifications may occur to those skilled in the art,particularly after benefiting from the present teaching, withoutdeparting from the spirit and scope thereof.

What is claimed is:

l. A method of producing chemical transformations in gases, comprisingthe steps of 1. moving a stream of gas at supersonic speed from adelivery zone to a collecting zone,

a. shock waves being produced at the outlet of the S delivery zone,

2. forming a supersonic gas cell in said stream between the delivery andcollecting zone,

b. the supersonic gas cell having a point of constricted cross sectionat which point the shock waves cause a deviation of the flow of thestream inwardly towards the axis of the gas stream,

3. positioning an axially extending principal electrode in the gasstream and surrounded thereby, the principal electrode extending throughthe delivery zone to the inlet of the collecting zone,

4. positioning an auxiliary electrode adjacent the gas stream,

5. producing an auxiliary electric discharge between said electrodes toionize the gas along the surface of the stream,

c. the gas ions on the surface of the stream being entrained inwardlyinto the stream at the point of constricted cross section, and

6. producing a principal electric discharge in the ionized gas stream bymeans of the principal electrode to produce a chemical transformation ofthe gas.

2. The method of claim 1, wherein the auxiliary electric discharge isproduced at the point closest to the inlet of the collecting zoneupstream of the point of constricted cross section.

3. The method of claim I, wherein the auxiliary electrode surrounds thedelivery zone and forms said steam at supersonic speed, the auxiliaryand the principal electrode are brought to an electric potential suchthat the difference between their potentials exceeds the difference ofthe potential between the principal electrode and a counterelectrodewherebetween the principal electric discharge is produced, the auxiliaryelectric discharge is produced between an end of the auxiliary electrodeand the principal electrode surrounded by the stream of gas, and theprincipal electric discharge is produced at the inlet of the collectingzone.

4. The method of claim 1, wherein voltages out of phase are applied tothe auxiliary and principal electrodes whereby the intensity of theauxiliary electric discharge is at a maximum when the voltage applied tothe principal electrode attains a value approximating that necessary tosustain the discharge in the ionized gas.

2. forming a supersonic gas cell in said stream between the delivery andcollecting zone, b. the supersonic gas cell having a point ofconstricted cross section at which point the shock waves cause adeviation of the flow of the stream inwardly towards the axis of the gasstream,
 2. The method of claim 1, wherein the auxiliary electricdischarge is produced at the point closest to the inlet of thecollecting zone upstream of the point of constricted cross section. 3.The method of claim 1, wherein the auxiliary electrode surrounds thedelivery zone and forms said steam at supersonic speed, thE auxiliaryand the principal electrode are brought to an electric potential suchthat the difference between their potentials exceeds the difference ofthe potential between the principal electrode and a counterelectrodewherebetween the principal electric discharge is produced, the auxiliaryelectric discharge is produced between an end of the auxiliary electrodeand the principal electrode surrounded by the stream of gas, and theprincipal electric discharge is produced at the inlet of the collectingzone.
 3. positioning an axially extending principal electrode in the gasstream and surrounded thereby, the principal electrode extending throughthe delivery zone to the inlet of the collecting zone,
 4. positioning anauxiliary electrode adjacent the gas stream,
 4. The method of claim 1,wherein voltages out of phase are applied to the auxiliary and principalelectrodes whereby the intensity of the auxiliary electric discharge isat a maximum when the voltage applied to the principal electrode attainsa value approximating that necessary to sustain the discharge in theionized gas.
 5. producing an auxiliary electric discharge between saidelectrodes to ionize the gas along the surface of the stream, c. the gasions on the surface of the stream being entrained inwardly into thestream at the point of constricted cross section, and
 6. producing aprincipal electric discharge in the ionized gas stream by means of theprincipal electrode to produce a chemical transformation of the gas.